A continuation of studies on the mechanisms by which myeloma proteins produce renal dysfunction and tubular cast formation. A number of Bence-Jones proteins from patients with myeloma and renal disease are being studied. These proteins are characterized as to type, subtype, internal structure, isoelectric point, co-precipitation with Tamm-Horsfall mucoprotein, and polymer-precipitate formation on partial proteolysis. They are further studied after injection into the rat under conditions of hydropenia, aciduria, and lysosomal enzymuria produced by prior tubular injury. It is thus hoped to delineate some of the factors responsible for renal dysfunction in myeloma.